The present disclosure relates to a rotor system, and more particularly to a lead stop which facilitates usage of a fluid-elastomeric lead/lag damper.
Hydraulic main rotor lead/lag dampers are utilized on many rotary wing aircraft. A single hydraulic lead/lag damper is mounted between each rotor blade and the rotor hub to minimize ground resonance by dissipating energy in the lead/lag direction. The hydraulic lead/lag damper has internal hard stops.
Of particular concern is rotor braking when the hydraulic lead/lag damper operates in conjunction with elastomeric blade retention bearings. As the rotor brake is applied, the rotor blade leads unrestricted until the hydraulic lead/lag damper bottoms out so that the blade centrifugal force and hydraulic lead/lag damper load react the rotor braking torque. The hydraulic lead/lag damper will only react the torque when fully extended. That is, the hydraulic lead/lag damper is bottomed out and essentially becomes a tension link.
As rotor speed and centrifugal force drop in response to rotor brake engagement, the rotor blade is pulled inboard into the rotor hub arm which results in inboard-directed tension loads. To react the inboard-directed tension loads, a lead stop assembly provides a contact surface between an inboard face of a droop stop bearing and a lead stop mounted to the hinge bearing plate of the rotor hub. Contact between an inboard face of the droop stop bearing and the lead stop only occurs when the hydraulic lead/lag damper is fully extended at a known, fixed position of about 10 degrees lead. This is the only position in which the hydraulic lead/lag damper is bottomed and can generate the detrimental inboard-directed tension loads. If the rotor braking torque is reduced for any reason and the rotor blade does not lead forward 10 degrees, then the hydraulic lead/lag damper will not bottom, does not operate as a tension link and will not generate the detrimental inboard-directed tension loads. This arrangement has been highly successful but is inapplicable to a fluid-elastomeric lead/lag damper which has a spring rate K which generates a load at every rotor blade lead/lag position.